Hi @Anonymous ,
Firstly, the "This formula uses scope, which is not presently supported for evaluation" prompt message is not an error, it is just a prompt message from the Formula Bar Intelligence.
Could you please share a bit more about your app's configuration? Do you add the Label inside a Gallery, and want to display the email value inside your Gallery?
The Office365Users.SearchUser() formula returns a Record value rather than Table value, if you want to check if the Office365Users.SearchUser() formula result is Blank, you should use the IsBlank() function. The screenshot as below:

Please modify your formula as below:
If(
IsBlank(Office365Users.SearchUser({searchTerm: name4.Text})),
"techsuppliermanagement@gmail.com",
ThisItem.Mail
)
If you want to display the value inside a Label , please set the Text property to above formula. If you want to display the value inside a Text Input Box, please set the Default property of the Text Input box to above formula.
Also please make sure the ThisItem.Mail formula could return a proper value. If you want to display corresponding email address based on the specific display name, please consider modify above formula as below:
If(
IsBlank(Office365Users.SearchUser({searchTerm: name4.Text})),
"techsuppliermanagement@gmail.com",
Office365Users.SearchUser({searchTerm: name4.Text}).Mail // Modify formula here
)
or
If(
IsBlank(LookUp(Office365Users.SearchUser(), name4.Text in DisplayName)),
"techsuppliermanagement@gmail.com",
LookUp(Office365Users.SearchUser(), name4.Text in DisplayName).Mail
)
Please consider take a try with above solution, check if the issue is solved.
Best regards,